1. Field of the Invention
The present invention relates to synthetic fibers used in the manufacture of non-woven fabrics. In particular, the present invention relates to polypropylene fibers intended for such use, processes of producing polypropylene fibers, compositions for producing polypropylene fibers, non-woven fabrics produced with polypropylene fibers, and articles containing polypropylene fibers.
2. Background Information
The production of polypropylene fibers and filaments usually involves the use of a mix of a single polymer with nominal amounts of stabilizers and pigments. The mix is melt extruded into fibers and fibrous products using conventional commercial processes. Non-woven fabrics are typically made by making a web of the fibers, and then thermally bonding the fibers together where they meet. More specifically, staple fibers are converted into non-woven fabrics using, for example, a carding machine, and the carded fabric is thermally bonded. The thermal bonding can be achieved using various heating techniques, including heating with heated rollers and heating through the use of ultrasonic welding.
Conventional thermally bonded non-woven fabrics exhibit good loft and softness properties, but less than optimal cross-directional strength, and less than optimal cross-directional strength in combination with high elongation. The strength of the thermally bonded non-woven fabrics depends upon the orientation of the fibers and the inherent strength of the bond points.
Over the years, improvements have been made in fibers which provide stronger bond strengths. However, further improvements are needed to provide even higher fabric strengths to permit use of these fabrics in today's high speed converting processes for hygiene products, such as diapers and other types of incontinence products. In particular, there is a need for a thermally bondable fiber and a resulting nonwoven fabric that possess high cross-directional strength and high elongation. Additionally, there is a need for a one-step process for making staple fiber known as a "short spin" process that provides filaments and fibers with properties as good as those produced by a two-step process called a "long spin" process.